Astronomy:Theta Hydri
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Hydrus |
| Right ascension | 03h 02m 15.449s[1] |
| Declination | −71° 54′ 08.84″[1] |
| Apparent magnitude (V) | 5.53[2] |
| Characteristics | |
| Spectral type | B8 III/IV[3] |
| U−B color index | −0.51[2] |
| B−V color index | −0.14[2] |
| Astrometry | |
| Radial velocity (Rv) | +12.3±1.6[4] km/s |
| Proper motion (μ) | RA: +27.256[1] mas/yr Dec.: +16.598[1] mas/yr |
| Parallax (π) | 6.4996 ± 0.0619[1] mas |
| Distance | 502 ± 5 ly (154 ± 1 pc) |
| Absolute magnitude (MV) | −0.48[5] |
| Details | |
| Luminosity | 287[5] L☉ |
| Surface gravity (log g) | 3.76[6] cgs |
| Temperature | 13,350[6] K |
| Rotation | 4.3720[7] d |
| Age | 211[8] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Theta Hydri, Latinized from θ Hydri, is the Bayer designation for a blue-white hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent visual magnitude of +5.53.[2] Based upon an annual parallax shift of 6.50 mas as seen from Earth,[1] is located approximately 502 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction of 0.10 due to interstellar dust.[8] It is moving away from the Sun with a radial velocity of +12.3 km/s.[4]
A stellar classification of B8 III/IV[3] suggests it is an evolving B-type star showing mixed traits of a subgiant or giant star. It is a PGa star – a sub-class of the higher temperature chemically peculiar stars known as mercury-manganese stars (HgMn stars). That is, it displays a rich spectra of singly-ionized phosphorus and gallium, in addition to ionized mercury and manganese. As such, Theta Hydri forms a typical example of this type. The absorption lines for these ionized elements are found to vary, most likely as the result of uneven surface distribution combined with the star's rotation.[10] It is a helium-weak star, having helium lines that are anomalously weak for its spectral type.[6] A weak and variable longitudinal magnetic field has been detected.[10]
There is a nearby companion star of class A0 IV[11] located at an angular separation of 0.1 arc seconds along a position angle of 179°, as of 2002. Schöller et al. (2010) consider this to be a visual companion,[12] although Eggleton and Tokovinin (2008) listed the pair as a probable binary star system.[11]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G. Gaia EDR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode: 1966CoLPL...4...99J.
- ↑ 3.0 3.1 Houk, N.; Cowley, A. P. (1975), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode: 1975mcts.book.....H.
- ↑ 4.0 4.1 de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics 546: 14, doi:10.1051/0004-6361/201219219, A61, Bibcode: 2012A&A...546A..61D.
- ↑ 5.0 5.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 6.0 6.1 6.2 Alonso, M. S. et al. (April 2003), "Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456*", Astronomy and Astrophysics 402: 331−334, doi:10.1051/0004-6361:20030222, Bibcode: 2003A&A...402..331A.
- ↑ Barraza, L. F. et al. (2022). "Rotation Signature of TESS B-type Stars. A Comprehensive Analysis". The Astrophysical Journal 924 (2): 117. doi:10.3847/1538-4357/ac3335. Bibcode: 2022ApJ...924..117B.
- ↑ 8.0 8.1 Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters 38 (11): 694−706, doi:10.1134/S1063773712110035, Bibcode: 2012AstL...38..694G.
- ↑ "tet Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tet+Hyi.
- ↑ 10.0 10.1 Hubrig, S. et al. (August 2014), "Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD 19400", Monthly Notices of the Royal Astronomical Society 442 (4): 3604−3615, doi:10.1093/mnras/stu1122, Bibcode: 2014MNRAS.442.3604H.
- ↑ 11.0 11.1 Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society 389 (2): 869–879, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode: 2008MNRAS.389..869E.
- ↑ Schöller, M. et al. (November 2010), "Multiplicity of late-type B stars with HgMn peculiarity", Astronomy and Astrophysics 522: 12, doi:10.1051/0004-6361/201014246, A85, Bibcode: 2010A&A...522A..85S
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